Use of betuline as a filler in paper and board

ABSTRACT

The invention relates to the use of betuline as a filler in paper or board, and to a method for producing paper or board. According to the invention, an aqueous slurry is made of betuline, followed by the addition of said slurry to the pulp during the production of paper or board, and removal of water from the paper web, and then the production of paper or board is continued in a conventional manner.

FIELD OF THE INVENTION

The present invention relates to the use of betuline as a filler inpaper and board, to a method for producing paper and board whereinbetuline is used as a filler, and further, to paper and board comprisingbetuline as a filler.

PRIOR ART

Mainly inorganic fillers such as kaolins, talc, silica, silicates,titanium dioxide, and calcium carbonates are used as fillers in paperand board, and moreover, to some extent fillers comprising organicpolymer pigments which may also be hollow. As examples thereof, polymerpigments based on urea/formaldehyde resins may be mentioned.

It is desired that the filler lowers the light scattering coefficientand tensile index of paper as little as possible. Among the inorganicfillers most commonly used, expensive titanium dioxide has an excellentlight scattering coefficient.

Within the European Union is under consideration that in the future, itwill be prohibited to dump compostable material to landfills. Then, theonly economically realistic alternative for the disposal of compostablewaste material will be incineration thereof. Inorganic pigments won't,however, burn, but produce ash residues dues as waste, whereas organiccompounds may be disposed of by incineration without waste residues.Moreover, within the EU, goals set concerning the proportion ofbioenergy in total energy production should be reached by 2010, andthus, combustible organic pigments are also desirable in this respect.

Great amounts of birch bark waste is produced annually by chemicalforest and sawmill industries, this waste being mainly disposed of byincineration. Betuline is found in birch bark, the content thereof inouter birch rind being about 20-40%. Betuline may be isolated frombirch, such as from the outer rind of the birch species Betula verrucosacommon in Scandinavia by extracting with organic solvents using methodsknown as such.

Betuline has a pentacyclic triterpene alcohol structure and it is alsoknown by the trivial name betulinol and by the systematc namelup-20(29)ene-3,28-diole. The structure of betuline is shown by thefollowing formula I:

Betuline is a white crystalline powder with a low density having astrongly hydrophobic nature, and it is hardly soluble in water.

Use of betuline in paper industry has been studied to some extent,particularly its effect on the yellowing of paper, brightness reversionof pulp, and its odour. In FI 10402, use of betuline as a coatingpigment of paper and board either alone or together with other pigmentsis discussed. A coating paste was made of betuline by slurrying ittogether with excipients in water in a similar manner as with talc andby stabilizing the slurry with a stabilizer. Coating pastes wereprepared from the slurry thus obtained using excipients known in theart, either with or without other coating pigments such as kaolin,calcium carbonate or talc. With this coating paste containing betuline,coated base papers having an improved light scattering could be madebecause of the fact that in the structure of betuline, there are, amongothers, hydroxyl groups necessary for the carriers of opticalbrighteners.

On the basis of the above discussion, it may be seen that there is aneed for papers and boards made from combustible raw materials, theproperties thereof, however, corresponding to those of papers and boardsprepared with conventional fillers, as well as for a method forproducing said papers and boards.

DISCLOSURE OF THE INVENTION

The invention is directed to the use of betuline as a filler in paperand board.

The invention also relates to a method for producing paper and board,comprising the use of betuline as a filler.

Moreover, the invention relates to papers and boards containing betulineas a filler.

Characteristic features of the use of betuline in the production ofpaper and board, the method for producing paper and board, and papersand boards containing betuline as a filler according to the inventionare presented in the claims.

BRIEF DESCRIPTION OF THE INVENTION

It was surprisingly found that problems and drawbacks of known solutionsof prior art may be solved or at least essentially avoided by usingbetuline as a filler in paper and board. In the production of paper orboard, betuline slurried in water is added to the pulp, preferably afterthe addition of retention aids, that is, as an aqueous slurry preferablycontaining betuline no more than 60% by weight, particularly preferablyfrom 5 to 35% by weight. Thus, paper and board that may be incineratedand having properties corresponding to those of papers and boards yetproduced with conventional fillers may be obtained.

DETAILED DESCRIPTION OF THE INVENTION

According to the invention, betuline may be used as a filler in paperand board, particularly as a filler in uncoated paper and board,preferably alone, but also together with known inorganic and/or organicfillers. An aqueous slurry is prepared from betuline and then, thisslurry is added to the pulp after the addition of retention aids duringthe production of paper or board. Preferably, no more than 60% byweight, particularly preferably from 5 to 35% by weight of betuline isdispersed in water with one or more excipients. One or more conventionalagents used for dispersion of hydrophobic compounds may be used asexcipients. Said adjuvants are preferably selected from a groupconsisting of dispersing agents, surface active agents and stabilizersthat stabilize the dispersion and prevent the formation of agglomerates.

Dispersing agent may be used in an amount ranging from 0 to 1% byweight, preferably from 0.01 to 0.4% by weight, the amount of thesurface active agent being 0 to 6% by weight, preferably from 2.5 to 5%by weight, and that of the stabilizer being from 0 to 1% by weight,preferably from 0.1 to 0.3% by weight. Useful dispersing agents includedispersing agents suitable for hydrophilic fillers such as salts of theacrylic acid polymers, examples of suitable surface active agentsinclude polyethylene glycols, and suitable stabilizers include polyvinylalcohols. Percentages by weight are calculated relative to the slurry.

If necessary, the pH of the slurry is adjusted with a base to a value ofat least 8.5, preferably between 8.5 and 10. Examples of suitable basesinclude inorganic bases such as NaOH, KOH and the like.

Betuline is preferably used as a fine powder having a mean particle sizeof no more than 30 μm, the particle size being preferably between 0.3and 10 μm, particularly preferably between 0.5 and 2.5 μm. A SEM imageof milled betuline particles is presented in the appended FIG. 1.

Betuline may be betuline prepared from birch, that is betuline isolatedfor instance by extraction from birch bark, from bark waste produced bypulp plants or industrial sawmills, or it may be synthetically producedbetuline. Betuline having a purity of at least 85% by weight, preferablyat least 95% by weight, is preferably used.

The method of the invention for producing paper or board comprises stepswherein an aqueous slurry is prepared containing preferably no more than60% by weight, particularly from 5 to 35% by weight of fine betulinethat is adjusted to a desirable particle size for instance by milling,if necessary, and then said slurry is added to the pulp used for paperor board production, particularly to fine paper pulp, preferably afterthe addition of retention aids. Then water is removed from the paper webfollowed by drying and calendering the paper or board if necessary, thatis, the production of paper or board is continued in a conventionalmanner known as such to those skilled in the art.

Pulp used in the production of paper or board comprises chemical pulp ormechanical pulp or a mixture thereof, preferably pulp for fine papersincluding softwood and hardwood pulps. Different pulps may be freelymixed depending on the product to be produced.

The paper or board of the invention comprises betuline as the filler,the amount of betuline in the paper or board ranging between 0.1 and60%, preferably between 5 and 35% by weight.

Betuline may be used as a filler in fine papers, in papers containingchemical and mechanical pulps, in uncoated and coated fine papers, incoated papers containing mechanical pulp, and moreover in the surfacelayers of boards, for instance in folding boxboard and linerboard.Preferably betuline is used in fine papers containing at present highamounts of inorganic fillers in conventional manner.

The present invention has considerable advantages compared to prior art.Retention of betuline is clearly higher than that of traditionalinorganic fillers. Due to this high retention of betuline, the qualityof recycled water is improved and purer recycled water is obtained andthus, lower amounts of fixing agents and retention aids are necessary.Formation is improved due to the reduction of retention aids. Inaddition, the examples show that in paper types containing betuline as afiller, the combination of tensile index and light scattering is clearlyimproved, and the tensile index may be increased in comparison toprecipitated calcium carbonate by about 40% without lowering the lightscattering coefficient. This is illustrated by FIG. 2. Interlaminarstrength of paper and board represented by Scott bond value is alsosomewhat increased.

Compared to the known precipitated calcium carbonate (PCC) fillerproviding high bulk, betuline surprisingly renders high bulk but lowporosity. Due to this low porosity, an impervious paper for coatinghaving a superior surface is obtained, and accordingly during thecoating step of the paper, clearly less coating paste is needed for highcoating power. Moreover, betuline prevents the pulp from yellowing asshown by the results of Example 3.

The density of betuline being low, it is a light-weight substance,whereas traditional inorganic pigments are heavy causing clearly higherlogistic costs than light-weight substances. With this light betuline,lighter printing and news quality papers may be produced, thus reducingmailing and other logistic costs and costs due to waste paper, andaccordingly, less waste detrimental to the environment is produced.

Unlike betuline, inorganic pigments do not belong to renewableresources. Betuline is an organic compound having a high heat value whenburned, and further, it does not produce ash. In addition, betuline hasantiviral, antifungal and antimicrobial activities, and thus the amountsof antimicrobial agents used in the production of paper and board may bereduced, which clearly lowers the environmental burden caused by saidagents.

The invention is now illustrated with the following examples withoutlimiting the scope of the invention thereto.

EXAMPLES Example 1 Dispersion of Betuline to Give a Slurry

Betuline was milled to give a fine powder having a mean particle size ofabout 1 μm. FIG. 1 shows the SEM image of the milled betuline. Then,0.15 parts by weight of a dispersing agent (Fennodispo A41), 3.5 partsby weight of a surface active agent (Lutesol T07), and 0.02 parts byweight of a 10% NaOH solution were added to water and mixed, followed bythe addition of 100 parts by weight of the milled betuline and 0.15parts by weight of a stabilizer (Celvol 103) to the mixture thusobtained. Then, the mixture was slurried for 40 minutes using a Diafdispersing apparatus.

Example 2 Preparation and Testing of Sheets Containing Betuline

For producing the sheets, 70% by weight of SR 21 birch pulp and 30% byweight of SR 27 softwood pulp were used. 0.3 mg/g of the retention aidPercol 47, relative to the absolute dry weight of the pulp, and from 5to 30% by weight of the betuline dispersion prepared in Example 1 wereadded to the pulp mixture. From the pulp thus obtained, normallaboratory sheets having a surface weight of 60 g/m² were made,compressed in conventional manner, dried and tested.

The sheets were extracted with acetone, followed by the determination ofthe amount of betuline by gas chromatography using an internal standard.Retention of betuline was rather high, the filler contents being 10% and20%. Control sheet 1 contained no filler, precipitated calcium carbonate(PCC) in scalenohedron form was used in other control sheets. Theretention of PCC was lower, and at best, filler contents were 8% and 3%.When comparing sheets containing 10% of betuline and 8% of PCC, it wasfound that betuline gave better strenght results, particularly thetensile index being clearly higher. Moreover, the porosity was betterwith betuline compared to control agents. The results are shown inTables 1 and 2 below, and in the appended FIG. 2, the tensile index ispresented as the function of the light scattering coefficient. TABLE 1Tensile Interlaminar Grammage, Thickness, Bulk, index, strenght/ScottPorosity, Sample g/m² μm cm³/kg kNm/kg bond, J/m² ml/min Control 1 59.576 1.27 49.0 450 470 Betuline 10% 64.8 107 1.64 71.5 300 950 Betuline20% 72.5 135 1.86 28.8 130 1350 PCC 3% 57.2 77 1.34 57.5 415 790 PCC 8%59.1 82 1.39 52.0 285 1030

TABLE 2 Grammage, Light scattering Sample g/m² Opacity, % coefficient,m²/kg Control 1 59.5 63.8 24.8 Betuline 10% 64.8 77.1 37.6 Betuline 20%72.3 86.2 53.5 PCC 3% 57.2 68.3 31.0 PCC 8% 59.1 73.3 37.9

Example 3 Preparation and Testing of Sheets Containing Betuline

Laboratory sheets having a surface weight of 60 g/m² were prepared fromchemical pulps containing respectively 10 and 20% by weight of betuline,and for comparison purposes, 3 and 8% by weight of PCC filler (AlcabarLO), the composition of the pulp being 70% by weight of birch and 30% byweight of tall.

FIGS. 3 and 4 show the results of the ISO brightness test and absorptioncoefficient test. The sheets containing betuline turned yellow clearlyslower than sheets containing PCC filler, and further, the sheetscontaining betuline were whitened more readily by light than othersheets. With respect to optical properties, the sheets containingbetuline corresponded to sheets containing the PCC filler.

1. Use of betuline as a filler in paper or board, wherein betuline isadded to the pulp during the production of paper or board.
 2. Useaccording to claim 1, characterized in that betuline is used incombination with organic and/or inorganic fillers.
 3. Method forproducing paper or board, characterized in that an aqueous slurry ismade of betuline, followed by the addition of said slurry to the pulpduring the production of paper or board, and removal of water from thepaper web, and then the production of paper or board is continued in aconventional manner.
 4. Method for producing paper or board according toclaim 3, characterized in that betuline is slurried in water togetherwith one or more excipients selected from the group consisting ofdispersing agents, surface active agents, and stabilizers.
 5. Method forproducing paper or board according to claim 3, characterized in that anaqueous slurry containing betuline is added to the pulp during theproduction of paper or board, after the addition of retention aids. 6.Method according to claim 3, characterized in that the aqueous slurrycontains no more than 60% by weight of betuline.
 7. Method according toclaim 3, characterized in that the aqueous slurry contains from 5 to 35%by weight of fine betuline.
 8. Method according to claim 3,characterized in that the aqueous slurry contains betuline having a meanparticle size of no more than 30 μm.
 9. Method according to claim 3,characterized in that the aqueous slurry contains betuline having a meanparticle size between 0.3 and 10 μm.
 10. Method according to claim 3,characterized in that the aqueous slurry contains betuline having a meanparticle size between 0.5 and 2.5 μm.
 11. Paper or board, characterizedin that it contains from 0.1 to 60% by weight, preferably from 5 to 35%by weight of betuline as the filler.
 12. Paper or board according toclaim 11, characterized in that it contains betuline in combination withinorganic and/or organic fillers as the filler.
 13. Method for producingpaper or board according to claim 4, characterized in that an aqueousslurry containing betuline is added to the pulp during the production ofpaper or board, after the addition of retention aids.
 14. Methodaccording to claim 4, characterized in that the aqueous slurry containsno more than 60% by weight of betuline.
 15. Method according to claim 5,characterized in that the aqueous slurry contains no more than 60% byweight of betuline.
 16. Method according to claim 4, characterized inthat the aqueous slurry contains from 5 to 35% by weight of finebetuline.
 17. Method according to claim 5, characterized in that theaqueous slurry contains from 5 to 35% by weight of fine betuline. 18.Method according to claim 6, characterized in that the aqueous slurrycontains from 5 to 35% by weight of fine betuline.
 19. Method accordingto claim 4, characterized in that the aqueous slurry contains betulinehaving a mean particle size of no more than 30 μm.
 20. Method accordingto claim 5, characterized in that the aqueous slurry contains betulinehaving a mean particle size of no more than 30 μm.